The present application is directed to a specific molecular system that involves at least one rotatable segment (rotor or rotors) that has a large dipole moment and that links with at least two other portions of the molecule that are immobilized (stators). The molecular system disclosed herein provides switching from one state to a different state, characterized by a change in the electronic properties and/or the optical properties of the molecules.
The present invention relates generally to electronic and optical devices whose functional length scales are measured in nanometers, and, more particularly, to classes of molecules that provide electronic and optical switching. Electronic and optical devices both of micrometer and nanometer scale may be constructed in accordance with the teachings herein.
The area of molecular electronics is in its infancy. To date, there have been two convincing demonstrations of molecules as electronic switches published in the technical literature; see, C.P. Collier et al., Science, Vol. 285, pp. 391-394 (Jul. 16, 1999) and C. P. Collier et al., Science, Vol. 289, pp. 1172-1175 (Aug. 18, 2000), but there is a great deal of speculation and interest within the scientific community surrounding this topic. In the published work, a molecule called a rotaxane or a catenane was trapped between two metal electrodes and caused to switch from an ON state to an OFF state by the application of a positive bias across the molecule. The ON and OFF states differed in resistivity by about a factor of 100 and 5, respectively, for the rotaxane and catenane.
The primary problem with the rotaxane was that it is an irreversible switch. It could only be toggled once. Thus, it can be used in a programmable read-only memory (PROM), but not in a ROM-like device nor in a reconfigurable system, such as a defect-tolerant communications and logic network. In addition, the rotaxane requires an oxidation and/or reduction reaction to occur before the switch can be toggled. This requires the expenditure of a significant amount of energy to toggle the switch. In addition, the large and complex nature of rotaxanes and related compounds potentially makes the switching times of the molecules slow. The primary problems with the catenanes are small ON-to-OFF ratio and a slow switching time.
Thus, what is needed is a molecular system that avoids chemical oxidation and/or reduction, permits reasonably rapid switching from a first state to a second, is reversible to permit the fabrication of ROM-like devices, and can be used in a variety of electronic and/or optical devices.
In accordance with the present invention, a molecular system is provided for nanometer-scale reversible electronic and optical switches, specifically, electric field-activated molecular switches that have an electric field induced band gap change that occurs via a molecular conformation change or a tautomerization. Changing of extended conjugation via chemical bonding change to change the band gap is accomplished by providing the molecular system with one rotating portion (rotor) and two or more stationary portions (stators), between which the rotor is attached.
The molecular system of the present invention has three branches (first, second, and third branches) with one end of each branch connected to a junction unit to form a xe2x80x9cYxe2x80x9d configuration. The first and second branches are on one side of the junction unit and the third branch is on the opposite side of the junction unit. The first branch contains a first stator unit in its backbone, the junction unit comprises a second stator unit, and the first branch further contains a rotor unit in its backbone between the first stator unit and the second stator unit. The rotor unit rotates between two states as a function of an externally applied field. The second branch includes an insulating supporting group in its backbone for providing a length of the second branch substantially equal to that of the first branch.
The present invention provides molecular reversible electronic and/or optical switches that can be assembled easily to make crossbar and other circuits. The crossbar circuits have been described in the above-listed series of patent applications and issued patent. The circuits provide memory, logic and communications functions. One example of the electronic switches is the so-called crossed-wire device, which comprises a pair of crossed wires that form a junction where one wire crosses another at an angle other than zero degrees and at least one connector species connecting the pair of crossed wires in the junction. The junction has a functional dimension in nanometers or larger for multilayers. The connector species comprises the molecular system disclosed and claimed herein.
The present invention introduces a new type of switching mechanism, namely, an electric field induced rotation of a rotatable middle section (rotor) of a molecule. Thus, the molecule is neither oxidized nor reduced in the toggling of the switch, which avoids the necessity of breaking chemical bonds and potentially initiating a nonreversible reaction. Also, the part of the molecule that moves is quite small, so the switching time should be very fast. Also, the molecules are much simpler and thus easier and cheaper to make than the rotaxanes and related compounds.
The devices of the present invention are generically considered to be electric field devices, and are to be distinguished from earlier embodiments (described in the above-mentioned related patent applications and patent) that are directed to electrochemical devices.
The present invention disclosure is an improvement over the foregoing applications and patent in that it is directed to a class of molecules that provides switching from one state to a different state, characterized by a change in the electrical conductivity. The three-branch or xe2x80x9cYxe2x80x9d configuration of the molecular switches creates an optical alignment between the dipole movement of the rotor and the direction of the electric field between the electrodes. Further, the xe2x80x9cYxe2x80x9d orientation allows the maximum interaction strength between the rotor dipole and the switching electric field.
The present invention disclosure relates generally to electronic and optical devices whose functional length scales are measured in nanometers, or larger and, more particularly, to classes of molecules that provide both electronic and optical switching. The electronic and/or optical devices both of micrometer and nanometer scale may be constructed in accordance with the teachings herein.